Freeness testing apparatus



Feb. 13, 1968 c. E. MILLER FREENESS TESTING APPARATUS INVENTOR. ClarenceE. Muller Filed Oct. 19, 1965 ATTORNEY United States Patent 3,368,392FREENESS TESTING APPARATUS Clarence E. Miller, Covingtou, Va., assignorto West Virginia Pulp and Paper Company, New York, N.Y., a corporationof Delaware Filed Oct. 19, 1965, Ser. No. 497,852 5 Claims. (Cl. 73-63)ABSTRACT OF THE DISCLOSURE In an in-line freeness testing device whichis mounted on a papermaking stock line and measures freeness byintermittently drawing samples of the stock into a standpipe having ascreen across its lower end and measuring the height to which the liquidrises in the standpipe in a given time, the sensitivity of measurementsis increased without increasing the length of the standpipe ordecreasing the volume of liquid sampled by using a standpipe having anupper portion of appreciably smaller cross-sectional area than its lowerportion.

The present invention is directed to apparatus for testing the freenessof paper stock and more particularly, to

apparatus of high sensitivity capable of indicating small changes inpaper stock freeness.

In the manufacture of paper, a low consistency slurry of fibers andliquid is deposited on a foraminous surface and the liquid allowed todrain, leaving a loosely felted mat of fibers. This mat is thereaftersubjected to pressing, driving, etc. to provide a finished paper web.Dependent to a great extent on the amount of refining to which thefibers are subjected is the rate at which the liquid will drain from theslurry. This characteristic is generally referred to as the stockfreeness, or, its antonym, slowness. Thus, a very free stock is usuallyone in which the fibers have been subjected to little refining and as aresult, the nbers are quite coarse and liquid will draintherefrom quitereadily. Conversely, a slow stock is generally one in which the fibershave been subjected to a great deal of refining and in consequence, thefibers are fine, com pact readily, and retard the rate of drainage ofthe liquid from the stock.

Aside from its obvious effect on process speed, it will be apparent thatthe freeness of a paper stock is also an indication of the quality ofthe paper which will be formed therefrom. It is therefore, highlydesirable to monitor and control the freeness of the paper stock duringthe paper making operation.

Unfortunately, in the past, a method of checking paper stock freenesswhich was both quick and accurate did not exist. Thus, one common methodof determining paper stock freeness is to withdraw a sample of the stockfrom the process and evaluate it in a laboratory. While the results areusually quite accurate, it will be obvious that the time intervalbetween withdrawing a sample and evaluating it greatly detracts from theeffectiveness of this method as a stock freeness control means.

More recently, apparatus has been designed which permits paper stockfreeness testing on an in line basis. Thus, as shown in U.S. Patent No.3,186,215, an elongated, hollow, standpipe is attached to a stock pipeline with a piece of screen or the like secured across its inlet endadjacent the pipe line. The other end of the standpipe is closed andconnected to a source of variable pressure. With this arrangement, itwill be seen, the interior of the standpipe may be kept under sufiicientpressure to prevent the stock from rising up into the standpipe. Atpreselected intervals however, this interior pressure is reducedsufiiciently to allow the stock to flow into the standpipe, the majorityof the fibers in the stock being filtered out by the screening acrossthe standpipe inlet. By either maintaining the reduced pressure for aset time period and observing the height to which the stock rises in thetube during that time, or allowing the stock to rise to a preselectedheight in the standpipe and measuring the time required for it to riseto that height, an indication of the freeness of the stock can beobtained.

One difliculty that has been experienced however, is that the smallchanges in stock freeness that will usually occur under normal operatingconditions are not readily discernible with this instrument; yet thesesmall changes will have an appreciable effect on the papermakingprocess. Thus, a fairly large change in freeness will result in only avery small change of liquid column height. To remedy this it has beensuggested that the internal diameter of the standpipe be reduced. Inthis way a change in freeness and hence, a change in the volume ofliquid entering the standpipe, will be reflected as an appreciablechange in liquid column height. It will be apparent though, that if thediameter of the standpipe is reduced, the length thereof must beincreased in order to accommodate the same volume of liquid. In practicehowever, it has been found that in order to decrease the diameter of thetube to a point where significant changes in liquid column height areobservable and at the same time retain the original capacity of thestandpipe, the length of the standpipe must be increased to an extentwhich is impractical in a commercial environment.

Another approach to increasing the sensitivity of the unit describedabove has been to decrease the tube diameter, retain its originallength, and shorten the sampling time, or the time in which liquid isallowed to rise in the standpipe, so that the volume of liquid which thetube must accommodate is decreased. Again, while this solution appearsattractive in theory, it has been found in practice that if the samplingtime is decreased to an extent sufficient to give the desired smallervolume, the resulting short sampling times do not permit theaccumulation on the inlet screen of a pad of fibers of sufficientthickness to give meaningful results.

It will be seen from the above, that while sampling and laboratorytesting provides an accurate method of checking stock freeness and inline testing is quick and convenient, neither method combines accuracywith speed and ease of operation.

It is therefore, an object of the present invention to provide means forquickly, accurately and automatically monitoring the freeness of paperstock or the like on an in line basis. This has been accomplished as aresult of applicants observation that although most commerciallyavailable equipment is capable of indicating freeness variations over afairly wide range of values, only relatively small changes will usuallyoccur in a commercial operation. Therefore, in a practical context, itis only necessary that the testing equipment be highly sensitive overthis relatively narrow range in order to obtain consistently accuratereadings.

On the basis of these observations applicant has devised means forimproving the sensitivity of prior art testing apparatus without.increasing standpipe length or reducing normal sampling time. Thus, itis a specific object of the present invention to increase thesensitivity of prior art freeness testing apparatus without sacrificingtheir convenience and ease of operation.

These and other features and objects of the present invention willbecome more readily apparent from the following detailed descriptionwherein:

FIGURE 1 is an elevational view, partly in section, of an embodiment ofthe present invention; and

. FIGURES 2 and 3 are illustrations of alternate embodiments of theinvention.

With reference to FIGURE 1 it will be seen that the improved freenesstesting unit may comprise an elongated, hollow member 1 formed in twomain sections 2 and 3 joined by a transition section 4. A suitablefitting 5 attaches the member 1 at its inlet end to a stock pipe line 6and a cap member 7 serves to close otf the opposite end of member 1. Asseen in FIGURE 1, section 2 of member 1 extends from the inlet endtowards the closed end thereof and is of subtsantially greater crosssectional area than any portion of section 3. A piece of screening orthe like 8 of a suitable mesh covers the inlet end of member 1 and apressure line 9 in conjunction with a pair of branch lines 10 and 11provides means for selectively pressurizing or depressurizing theinterior of member 1. Lines 10 and 11 each pass through a timer unit 12and thence, to a pressure source and a source of vacuum or atmosphere,respectively. A pressure cell 13 is attached to member 1 adjacent itsinlet end and signals received by cell 13 aretransmitted for recordingto a recorder 14.

In operation, the interior of the member 1 may be kept under sufficientpressure by means of lines 9 and 10 to prevent the stock 15 from risingup into member 1. At preselected intervals however, timer unit 12 closesoff line 10 and through lines 9 and 11 provides a sufliciently reducedpressure within member 1 to allow the stock to flow thereinto. Timerunit 12 may be adjusted to maintain this reduced pressure for a presetsampling time, and at the end of this period, the interior of member 1is again pressurized, forcing the stock liquid back into the pipe line 6and flushing off the pad of fibers which has collected on screening 8.Recording unit 14, through signals received from pressure cell 13, hasmeanwhile recorded the maximum pressure which occurred in the memberduring the period of reduced pressure.

As noted previously, in prior art apparatus of this type a constantdiameter tube or standpipe was used, and in order to maintain the lengthof the tube within reasonable limits and at the same time permit theaccommodation of a sufficient volume of liquid in the standpipe to allowa pad of fibers to build up on the screened inlet, the diameter of thetube was fairly large. However, with a large diameter tube, anappreciable change in freeness and hence, a proportionate change in thevolume of the liquid entering the tube, resulted in very little changein liquid column height.

By means of the present invention however, it will be seen that therelatively large cross sectional area of section 2 allows a large enoughvolume of liquid to be accommodated in member 1 to permit the build upof a pad of fibers on screen 8 of sufficient thickness to givemeaningful readings. At the same time, the overall length of member 1need not be increased. On the other hand, in section 3 of member 1, arelatively small change in the volume entering this section will resultin an appreciable change in liquid column height. Since, as a practicalmatter the changes in freeness which will normally occur will be quitesmall and hence, the changes in the volume of liquid entering member Iquite small, member 1 can readily be dimensioned so that the terminationof a sampling cycle will occur while the liquid level is within section3. Since the pressure sensed by cell 13 is determined by liquid columnheight, irrespective of volume, the reduced cross sectional area ofsection 3 provides an extremely sensitive indication of changes in thevolume of liquid passing into member 1 and hence, of the freeness of thestock in pipe line 6.

While for simplicity of manufacture a configuration I such as that shownin FIGURE 1 Will usually be preferred, it will be apparent that theelongated, hollow member 1 may take a variety of shapes within the scopeof the invention. For example, as seen in FIGURE 2, substantiallyspherical section 2a of member 111 has a portion of substantiallygreater cross sectional area than any portion of cylindrical section 3a.As a result, a large volume of liquid may be accommodated in member 1a,as in member 1, yet relatively small changes occurring towards the endof the sampling cycle are reflected as relatively large changes inliquid column height by the reduced cross sectional area of section 3a.

Similarly, while the relatively large cross sectional area of at least aportion of section 2b, FIGURE 3, permits a large volume of liquid to beaccommodated by the elongated, hollow member 112, relatively smallchanges in volume occurring in section 312 will result in readilydiscernible changes in pressure readings on a recorder of the type shownin FIGURE 1.

From the foregoing it will be apparent that applicant has improved thesensitivity of prior art freeness testing apparatus in a manner suchthat its convenience and ease of operation are not reduced. Whilecertain specific examples of the invention have been described forpurposes of illustration, modifications thereof will readily occur tothose skilled in the art within the scope of the appended claims.

I claim:

1. In apparatus for testing the freeness of paper stock, including astandpipe with an open lower end, a horizontal screen mounted across thebase portion of said standpipe for separating the fibers from the liquidof said paper stock, means connected to said standpipe for reducing thepressure therein and causing liquid from said paper stock to rise intosaid chamber while said fibers form a mat on said screen, and means formeasuring the rate at which said liquid rises into said standpipethrough said screen as an indication of relative stock freeness, theimprovement comprising:

(a) said standpipe being formed in at least two sections,

(b) a first of said sections extending from said open lower end towardthe opposite end thereof,

(c) the other of said sections extending from said opposite end towardsaid open lower end,

((1) at least a portion of said first section being of substantiallygreater cross-sectional area than said other section.

2. The apparatus of claim 1 wherein:

(a) both of said sections are substantially cylindrical,

and

(b) the internal diameter of said first section is substantially largerthan the internal diameter of said other section.

3. The apparatus of claim 2 wherein:

(a) a hollow, tapered transition section interconnects said cylindricalsections.

4. The apparatus of claim 1 wherein:

(a) said first section is substantially spherical in shape,

(b) said other section is substantially cylindrical in shape, and

( the internal diameter of said first section is substantially largerthan the internal diameter of said other section.

5. The apparatus of claim 1 wherein:

(a) said first section tapers from a maximum internal dimension adjacentsaid open, inlet end to a minimum internal dimension adjacent said othersection,

(b) said other section is substantially cylindrical in shape, and

(c) said minimum dimension and the internal diameter of said othersection are substantially the same.

References Cited UNITED STATES PATENTS 1,624,659 4/1927 Eynon 73-2993,186,215 6/1965 Danforth 7363 FOREIGN PATENTS 392,766 3/ 1924 Germany.

DAVID SCHONBERG, Primary Examiner.

